The present invention relates to a sorter which is installed in an image forming apparatus such as a copying machine, a printing machine or a laser beam printer and receives sheets ejected from the image forming apparatus after separating and sorting them, and more particularly, to a sorter equipped with a number of bins and with a stapler unit that staples sheets stacked on each bin after aligning the edges of the sheets.
Heretofore, as a sheet finisher equipped with a stapler unit that staples sheets ejected from a copying machine or the like, there has been a sheet finisher which is used together with a machine such as an automatic recirculating document handler (RDH) or the like and staples each stack of sheets. Such a sheet finisher, however, has a drawback that its structure is complicated and its cost is high.
(1) In Japanese Patent Publication Open to Public Inspection No. 43457/1989 (hereinafter referred to as Japanese Patent O.P.I. Publication), has disclosed an apparatus in which a stapling device is provided to a relatively simple bin-moving type of sorter. In the aforementioned apparatus, a stapling device to staple sheets sorted into a bin can be freely moved with regard to the bin.
(2) Another sorter is composed in such a manner that: a fixed type of stapling device is provided to each bin; and the bin is moved to the stapling position so that a stack of sheets can be stapled.
(3) A sorter disclosed in Japanese Patent O.P.I. Publication No. 244869/1987, is composed in such a manner that: a bin having sheets is moved horizontally and straight to a position where a stapling operation can be conducted; the sheets are stapled by a stapling device; and when the sheets in other bins are stapled, the stapling device is moved in a vertical direction.
In the aforementioned sorter of case (1) having a stapling device which can be moved freely, the moving stroke of the stapling device is different according to sheet size. Accordingly, when vertical spacing of each bin is set large, the sorter size becomes large as a whole, and when vertical spacing of a bin into which the stapling device is inserted, is extended, the mechanism becomes complicated.
In the aforementioned sorter of case (2), the structure of the sorter is complicated as a whole, and in the case where a vertical spacing of the bin is small, a special stapling device is required.
In the aforementioned sorter of case (3), each bin in which sheets are put, is moved straight along a bin guide at an appropriate time. Accordingly, it is disadvantageous in that the structure becomes complicated.
In any of the sorters mentioned above, considerably long time is needed for the period from delivery of a sheet from the image forming apparatus into each bin to the completion of stapling.
Further, in the conventional system, a stapler is moved toward the bin for the succeeding stapling after a certain predetermined period of time has passed from the completion of the preceding stapling operation. Therefore, even when a stack of stapled sheets has not returned to the right position due to the phenomenon that the sheets in a stack are bent or caught, the stapler is forcibly caused to start moving after the predetermined time has passed, resulting in the possibility that the stapler may hit the bin or paper jamming may be caused.
The following two methods are generally used for moving a moving body up and down vertically.
(1) Two wires suspend the moving body, and a driving means connected to the wires drives the moving body in a vertical direction. PA0 (2) Rotatable rollers are provided on a moving body so that the rollers slide on fixed guide rail surfaces and the moving body is suspended with a single chain. PA0 (1) a supporting shaft fixed to the main body of the sorter in an upright position for rotatably supporting the plurality of bins at regular intervals. PA0 (2) a hole provided through the bin at a portion near one end of the bin, through which the supporting shaft is inserted, thereby the hole functions as the center of rotation of the bin. PA0 (3) a peripheral portion of the bin on the other end of the bin to which force is applied to rotate the bin. PA0 (4) means for rotating the bin from a stacking position to a stapling position by pushing the peripheral portion, in which the stacking position is suited to receive the recording sheet and the stacking position is suitable for the sheet stack to undergo the stapling. PA0 (5) a stapling unit movable to a plurality of stapler positions along an upright direction. PA0 (6) means for detecting a trailing edge of the sheet. PA0 (7) counter means for counting a number of sheets transferred to each bin, wherein the acceptance of the last sheet by each bin is acknowledged by the logical product of the detection of the trailing edge and a counting up of a predetermined number of sheets to be stacked on each bin.
When the conventional methods for moving up and down the moving body mentioned above, are used as a means for moving up and down a stapler, the following problems are caused.
In the method (1) wherein a moving body is suspended with two wires, a play between the moving body and an outer body is large and the moving body is apt to swing, resulting in an unstable stopping position of the body and consequent dispersion in the stapling position on sheets.
In the method (2) wherein rollers and guide rails are used for moving a unit body, the play is also large, resulting in a great disparity in the stapling position on sheets, which is a serious problem.
The play is a problem for both methods of (1) and (2), and when a guide rail or the like is provided additionally for eliminating the play, the sliding friction for the vertical movement of the unit body is caused and a motor having a large torque is required, which is a problem.